The current study was designed to examine patterns of morning cortisol production among maltreated foster children compared to their nonmaltreated peers. Overall, there were two noteworthy findings. First, the results of this study provide corroborating evidence that early adverse experiences have a significant impact on the HPA system. As was hypothesized, the foster children displayed significantly lower morning cortisol levels than the nonmaltreated children. Furthermore, when the children’s morning cortisol levels were classified as low, average, or high, nearly one third of the foster children (more than twice the percentage of nonmaltreated children) were in the low cortisol classification group. These results are consistent with research involving nonhuman primates exposed to repeated maternal separations, children raised in institutions, and children placed in foster care as infants (Carlson & Earls, 1997
; Dozier et al., 2006
; Sáchez et al., 2005
). Taken in combination, these studies support the conceptualization that blunted morning cortisol levels are a likely consequence of chronic stress and chronic activation of the HPA system (Fries et al., 2005
; Gunnar & Vazquez, 2001
; Heim, Ehlert, et al., 2000
). Although the exact mechanism is not known, it has been proposed that chronic elevations in corticotrophin-releasing factor (CRF), a hypothalamic secretogogue that begins the hormonal cascade of the HPA system, result in an adaptive down-regulation of CRF receptors in the pituitary and ultimately blunted cortisol levels (Heim, Ehlert, et al., 2000
; Heim et al., 2001
). However, there is a need for research examining the counterregulatory mechanisms underlying the low morning cortisol levels observed among these populations.
Second, the results from the current study suggest that specific early adverse experiences differentially affect the HPA system. That is, although the foster children were more likely to exhibit low morning cortisol levels, there was a great deal of heterogeneity within the foster sample. Notably, individual differences in morning cortisol levels were associated with different maltreatment experiences. Consistent with prior research with neglected children (Carlson & Earls, 1997
; Dozier et al., 2006
), foster children with histories of severe physical neglect were more likely to have low morning cortisol levels. In contrast, foster children who had experienced severe emotional maltreatment were more likely to have high morning cortisol levels. This result is consistent with prior research findings that depressed, school-aged children who were experiencing ongoing, severe emotional maltreatment demonstrated increased activation of the HPA system in response to pharmacological manipulation (Kaufman et al., 1997
). In the current study, morning cortisol levels were not significantly associated with severity of physical abuse, sexual abuse, or supervisory neglect or with number of caregiver disruptions.
A possible explanation for the differential effects of physical neglect and emotional maltreatment is that these experiences represent different types of stressors. That is, it has been suggested that chronic stress results in decreased cortisol production, whereas acute stress results in increased cortisol production (Fries et al., 2005
). In the current study, severe physical neglect involved parental failure to meet the children’s physical needs and to provide responsive caregiving. Such unresponsive caregiving might also fail to buffer young children from stressors and chronic activation of the HPA system (Gunnar & Donzella, 2002
; Gunnar et al., 2006
). As such, physical neglect might be considered a pervasive, chronic stressor. In contrast, emotional maltreatment included parental rejection and failure to protect children from witnessing traumatic events. Emotional maltreatment of this nature might be characterized as a periodic, acute stressor. Although this explanation is consistent with the conceptualization formulated by Fries and colleagues (2005
), additional research is needed to understand the nature of these maltreatment experiences. Such research might prove beneficial in moving toward more defined conceptual models with specific early adverse experiences contributing to specific outcomes.
There are a number of potential implications of the different patterns of morning cortisol production observed among foster children. Because elevated morning cortisol levels mobilize energy resources, children with low morning cortisol levels might lack the needed resources to undertake the processes involved in learning and socialization (Gunnar & Vazquez, 2001
). In addition, because cortisol has an immunosuppressive action, low cortisol levels might result in increased vulnerability to autoimmune disorders (Heim, Ehlert, et al., 2000
). Finally, low diurnal cortisol levels have been observed in adolescent males with externalizing behaviors and adults with posttraumatic stress disorder (Shirtcliff, Granger, Booth, & Johnson, 2005
; Yehuda, Halligan, & Bierer, 2002
). In contrast, elevated cortisol levels have been shown to impair cognitive processes, particularly vigilance and memory (Lupien et al., 2007
). Elevated cortisol levels also suppress immune and inflammatory reactions, leaving individuals vulnerable to illnesses and infections (Sapolsky et al., 2000
). Finally, a number of studies have reported elevated diurnal cortisol levels among individuals with affective disorders (Gold, Goodwin, & Chrousos, 1988
; Plotsky, Owens, & Nemeroff, 1998
). Thus, both low and high morning cortisol levels might be dysfunctional and might place foster children at risk for a host of difficulties.
Conversely, elevated diurnal cortisol levels among foster children might be an adaptive response to neglectful and/or abusive environments (Tarullo & Gunnar, 2006
). That is, the capacity to mobilize the HPA system might reflect an active attempt to cope with stressful living conditions. Indeed, Cicchetti and Rogosch (2007)
found high morning cortisol levels among physically abused children to be associated with higher resilient functioning. Similarly, high morning cortisol levels might be an adaptive response to the unpredictable, acute stressors experienced within emotionally maltreating environments. However, it is likely that this initially adaptive pattern of cortisol production would be less adaptive in new environments and would be detrimental to the children over time.
It is notable that severity of sexual abuse was not significantly related to the foster children’s morning cortisol levels in the current study. This result diverges from a prior study that found a positive association between severity of sexual abuse and morning cortisol levels (Cicchetti & Rogosch, 2001
). There were, however, several differences between the two studies. Specifically, the sample for the current study included preschool-aged maltreated foster children rather than school-aged maltreated children and the cortisol samples for the current study were collected at the children’s homes rather than at a day camp. Thus, future research should explore whether the discrepant results were due to developmental or contextual differences. For example, the morning cortisol levels in the prior study might reflect the children’s responses to a novel environment and peer group rather than their typical diurnal pattern.
In the current study, the foster children’s morning cortisol levels were also not related to their foster care placement experiences. Similarly, Dozier and colleagues (2006)
reported a lack of association between morning cortisol levels and foster care placement experiences. Taken together, these results suggest that specific maltreatment experiences impact the development of the HPA system more strongly than foster care placement experiences.
The results of the current study raise many questions for future research. Because of ethical and methodological issues, most research with young foster children has focused on measures of diurnal cortisol. Although chronic stress appears to result in low morning cortisol levels, it is not appropriate to assume a similar effect on the system’s response to psychological or pharmacological challenges. For example, although women with histories of childhood abuse have been shown to exhibit low diurnal and pharmacologically stimulated cortisol levels, they have also been shown to demonstrate more typical cortisol responses to a psychological stressor (Heim et al., 2001
; Heim, Newport, et al., 2000
). Additionally, it will be important to examine the malleability of the HPA system following a change in the environment. Interestingly, research with rodents has shown that environmental enrichment later in life ameliorates the effect of maternal separations on stress reactivity (Francis, Diorio, Plotsky, & Meaney, 2002
). Furthermore, as is noted above, the children in the current study participated in a randomized efficacy trial of a family-based preventive intervention program. Results of this efficacy trial have demonstrated that the intervention might be effective in preventing the increasingly dysregulated morning cortisol levels observed among the foster children who did not receive the intervention (Fisher & Stoolmiller, in press
; Fisher et al., 2007
In summary, maltreated foster children showed significant alterations in their morning cortisol production compared to nonmaltreated children. Although low morning cortisol levels were the characteristic pattern observed in the foster children, morning cortisol levels varied depending upon their maltreatment experiences. Specifically, the foster children with low morning cortisol levels had experienced more severe physical neglect, whereas the foster children with high morning cortisol levels had experienced more severe emotional maltreatment. Physical abuse, sexual abuse, and supervisory neglect did not appear to impact morning cortisol levels. Overall, these results suggest that the HPA system responds differentially to specific types of early adverse experiences.